1. Field of the Invention
The present invention relates to a device for controlling a touch panel, and more particularly, to a device for controlling a touch panel, which maintains the quantity of current output from a differential amplification unit at an appropriate level in order to prevent plus and minus power supply voltages from clamping due to saturation of the output signal of the differential amplification unit when an excessively large quantity of current is output from the differential amplification unit, to thereby generate no distortion in the output signal of the differential amplification unit and detect a correct touched point irrespective of the level of conductivity of an object touching a touch panel.
2. Background of the Related Art
With the development of computers using digital technologies, peripheral devices also have been developed. The computer peripheral devices include a monitor, a keyboard, a mouse, a microphone, speakers and so on. Particularly, the keyboard and microphone are used to input external data to a computer. Specifically, the keyboard inputs data to the computer in a manner that its keys are pushed and the microphone inputs data using its user's voice. However, the more effective and easier method for inputting data to the computer is that a user touches the screen of the monitor connected to the computer to input data to the computer. For example, it is easier for the user to produce graphics on paper using a pen than the keyboard or mouse. Thus, it is inconvenient for the user to produce graphics using the computer.
However, when the user directly processes graphics on a touch panel using a touch pen, he/she can process the graphic work very easy and delicately. Accordingly, portable devices including the touch panel are replacing the peripheral devices such as the keyboard and mouse. For example, PDA (Personal Digital Assistant) includes a touch panel and a touch pen instead of a keyboard having keys by which users manually input data such that the user operate the touch panel using the touch pen to input data or commands.
When people touch the touch panel in a prior art, however, a constant quantity of current is applied to the touch panel all the time. Accordingly, an excessively large quantity of current flows when a person with high conductivity touches the touch panel and a correct touched point cannot be detected when a person with low conductivity touches the touch panel.